In the early history of power transmission chain, inverted tooth or silent chain was constructed of sets of links connected together at articulating joints by circular pins. Later, the pin was replaced with a two-part joint comprising a pin and a rocker having abutting surfaces, one of which is rockable on the other. Various configurations of pins and rockers have been suggested in the prior art. For example, U.S. Pat. No. 3,213,699, granted to Terepin describes a pin and rocker joint constructed with pins and rockers substantially identical to each other in section. Each pin and rocker taught by the Terepin patent has an arcuate rocking surface, and an arcuate back surface substantially concentric with the rocking surface. When assemblying a chain with such a pin and rocker configuration, it is possible by rotating a pin or rocker through 180.degree., to improperly position it in the link apertures. This may not be detected upon inspection, and leads to early chain failure and improper operation. Because each of these components has only one rocking surface suitable for rocking engagement with the other, when this surface becomes worn, both components must be replaced.
A later U.S. Pat. No. 3,742,776 granted to Avramidis describes a chain in which the pin and rocker elements are substantially identical in section which are "wedged" into the apertures.
Still another advance is described in application Ser. No. 440,440, filed Feb. 7, 1974, entitled "Power Transmission Drive" issued Mar. 8, 1977 as U.S. Pat. No. 4,010,656. The chain of this application is characterized by having convex hypotrochoid pins and rockers of substantially similar section which are received in ovate or egg-shaped, elongated apertures in the links. The small end of the aperture receives a pin or rocker, as the case may be, in seated engagement.